As is well known in the art, gasification technology is a clean energy production technology of producing syngas by gasifying coal, biomass or low-grade hydrocarbon fractions such as heavy residual oil. The produced syngas is used in IGCC (Integrated Gasification Combined Cycle), for the production of chemical materials such as methanol or DME (dimethyl ether), synthetic petroleum and synthetic natural gas, or the like.
Typical examples of conventional coal gasifiers include slagging gasifiers that are operated at a temperature of 1,400° C. or higher, and fluidized-bed or fixed-bed gasifiers that are operated in a non-slagging mode.
Organic substances such as coal or heavy residual oil can be converted into syngas at a temperature 1,300° C., whereas slagging gasifiers are operated in the temperature range from 1,400 to 1,600° C. in order to melt ash. Unlike these gasifiers, fluidized-bed or fixed-bed gasifiers are operated at a temperature of 1,000° C. or below, which is lower than the slagging temperature of ash, in order to avoid the adhesion of ash upon slagging.
Most gasification technologies designed to gasify solid particle materials such as coal, or ash-containing liquid materials such as heavy residual oil, to produce clean energy, are based on entrained-bed gasification technology in which pulverized coal particles having a very small size are entrained into a stream of an oxidizer (oxygen or a mixed gas of oxygen and steam) to promote gasification reactions.
In most gasification technologies, as a relatively large amount of an oxidizer is supplied, the operating temperature of the gasifier is as high as 1,400 to 1,600° C., and the gasification reaction is performed in this high-temperature atmosphere. Thus, there is an advantage in that the time required for the reaction is short.
In addition, entrained-bed gasification technology uses a technology of slagging ash in this high-temperature atmosphere to form slag.
Thus, entrained-bed gasification technology has an advantage in that the conversion rate of carbon is high, because the carbon of pulverized coal is mostly converted into a gaseous state in a process in which most pulverized coal flows along the inner wall of the gasifier in a molten state.
On the other hand, in the case of such entrained-bed gasifiers, a reactor manufactured by lining a thick refractory material on the inner wall of a pressure vessel in order to protect the gasifier from high-temperature molten slag is frequently used.
Because the high-temperature molten ash slag flows along the wall surface of the gasifier, the refractory material is damaged by corrosion within a relatively short time. Further, syngas, which results in the gasification reaction of raw material and contains carbon monoxide (CO) and hydrogen (H2) as main components, also contains sulfur-containing gas such as corrosive hydrogen sulfide (H2S), which increases the corrosive property of the high-temperature syngas to significantly shorten the life span of the refractory material.
Indeed, in the case of many commercial gasification plants, the life span of the refractory material is short, and thus significant cost and time are required in a process of replacing the refractory material with fresh refractory material, thus reducing the availability of commercial plants.
As a result, due to the short life span of the refractory, in an integrated gasification combined cycle (IGCC) system in which pulverized coal is gasified to operate a combined power plant, the number of annual operating days is reduced, thus causing problems in terms of economy. In addition, in a plant in which synthetic petroleum or chemical materials are produced using syngas produced by gasification of pulverized coal, the annual production of products is reduced, thus causing problems in terms of economy.
Technologies contrary to such slagging-type gasifiers include non-slagging type gasification technologies, and typical examples of the non-slagging type gasification technologies include fluidized-bed gasification technologies.
In all the fluidized-bed gasification technologies, a solid fluid medium (usually sand or coal ash) is additionally supplied so that an oxidizer and crushed coal particles are brought into direct contact and mixed with the solid fluid medium in the reactor to promote the gasification reaction.
However, in such fluidized-bed gasification technology, the fluid medium should not melt, and for this reason, the oxidizer is supplied in a relatively small amount compared to that in the case of the entrained-bed gasifier, and thus the operating temperature of the fluidized-bed gasifier is generally about 950° C. or lower and does not exceed 1000° C. Thus, the fluidized-bed gasification technology has an advantage in that the life span of the refractory material is long.
However, fluidized-bed gasification technology has disadvantages in that the gasification reaction is time-consuming due to the low operating temperature compared to that in entrained-bed gasification technology and in that the conversion rate of carbon is low compared to that in entrained-bed gasification technology.
In addition, it has disadvantages in that the size of the reactor is required to be increased in order to compensate for the low operating temperature, and as the size of the reactor increases, the area of the outer wall of the reactor, which comes into contact with the atmosphere, also increases, resulting in an increase in heat loss. Furthermore, due to the relatively low operating temperature, the raw material is not completely converted into syngas, and some amount of liquid tar is produced to cause operation failure or reduce yield.
In some cases, fouling occurs to cause operation failure.
Regarding the background of the present invention, for example, Korean Patent Registration No. 10-1096632 (published on Dec. 21, 2011) discloses a top-feeding dual-swirling gasifier comprising: a feed line through which pulverized coal is fed by nitrogen; a distributor configured to divide pulverized coal being fed; a plurality of burner nozzles configured to feed the pulverized coal divided in the distributor and an oxidizer; a pressure reactor configured to react pulverized coal with the oxidizer to produce syngas containing carbon monoxide (CO) and hydrogen (H2) as main components; a swirl generator configured to impart a swirling force to the oxidizer that is fed into the pressure reactor; a slag cooling and storing container placed beneath the pressure reactor, wherein each of the burner nozzles for feeding the pulverized coal and the oxidizer consists of a triple tube. The pulverized coal and a carrier gas are supplied to the central region, and the oxidizer is supplied to an annular region surrounding the central region.
According to this configuration, as the oxidizer is imparted with a swirling force by the swirl generator in the annular region, the mixing of the raw material pulverized coal and the oxidizer is promoted, thereby achieving rapid completion of the gasification reaction. As a result, the volume of the gasifier is reduced, and slag formed by the slagging and agglomeration of the pulverized coal particles flows along the inner wall of the gasifier due to a centrifugal force created by the swirling flow while it resides in the reactor for a long time, and thus the conversion rate of carbon is increased. Furthermore, the pulverized coal particles can be treated to form a slag byproduct, and thus economy is ensured.
The above patent relates to an entrained-bed gasifier that is operated in a slagging mode. According to the disclosure of the patent, an integral burner unit consisting of a plurality of triple tube type burners is disposed at the top of the gasifier, and a material supply line is disposed in the central region of each burner to inject pulverized coal. Also, a swirl generator is disposed in an annular region surrounding the material supply line to impart a swirling force to a primary oxidizer flowing around the material to thereby form a swirl flow in the gasifier, and cooling water flows to the annular region of each burner to protect the burner from a high-temperature environment. In addition, a secondary oxidizer is supplied to a portion of the circular cross-section area of the top of the gasifier, which excludes the region in which the plurality of burners are disposed, in such a manner that a swirling force can also be imparted to the secondary oxidizer. In addition, as the flow rate of the primary oxidizer and the flow rate of the secondary oxidizer can be separately controlled, the raw material is supplied through the plurality of burners, and a swirling force is imparted to the primary oxidizer supplied from each burner while it is also imparted to the secondary oxidizer flowing through the region surrounding the burners, whereby the flow of the pulverized coal is inclined toward the inner wall of the gasifier, and thus ash present in the pulverized coal can mostly be treated in a molten state, thereby increasing the conversion rate of carbon.
Conventional entrained-bed gasification technologies including the above patent adopt slagging-type technology and have the advantages as described above.
However, although conventional entrained-bed gasification technologies have the advantages as described above, an excellent refractory material that can resist the high-temperature environment of the entrained-bed gasifier for a time of 1 or 2 years or longer does not exist, and a very special material is required, and the price thereof is not suitable for commercial applications. In view of these facts, the gasifier cannot be operated for a long period of time in an environment in which corrosion by molten slag that excessively moves toward the inner wall of the gasifier, in addition to corrosion by syngas, occurs.
In fluidized-bed gasification technology that is conventional technology belonging to another class, the operating temperature of the fluidized-bed gasification technology is about 950° C. or below, at which ash is not melted, and the operating temperature does not exceed 1000° C. For this reason, this technology has an advantage in that the life span of the refractory material is long, and thus long-term operation is possible, whereas it has disadvantages in that, due to this low operating temperature, it requires a large amount of time for the gasification reaction compared to entrained-bed gasification technology, the conversion rate of carbon is lower than that in entrained-bed gasification technology, and the size of the reactor is required to be increased.
In addition, due to the low operating temperature, some amount of liquid tar is produced to cause operation failure or reduce the yield, and in some cases, fouling occurs to cause operation failure.